1. Field of the Invention
This invention relates to a control for a mechanism which adjusts the position of a passenger loading bridge relative to a door on an aircraft.
2. Description of the Prior Art
A passenger loading bridge provides an enclosed passage for passengers to walk between a terminal building an an aircraft, as shown in U.S. Pat. Nos. 3,038,185; 3,184,772 and 3,358,308. Aircraft passenger loading bridges come in a wide variety of types and sizes. Some bridges have a fixed length and are pivotable radially about a fixed pivot between a stowed position and an aircraft engaging position, some bridges can be telescoped longitudinally and are pivotable radially about a fixed pivot and some bridges have a fixed length and are mounted on a stationary pedestal. An aircraft engaging cab is mounted on the distal end of each of the aforementioned types of bridges.
Each type of bridge has a mechanism for adjusting the vertical height of the cab at the distal end of the bridge. The height adjustment mechanism enables an operator to change the height of the distal end of the bridge so that the cab engages the doors of different types of aircraft at the proper location.
The height adjustment mechanism may be electromechanical, as where a motor drives a ball screw which raises or lowers the distal end of a bridge, or it may be electrohydraulic, as where a motor drives a pump which supplies fluid to extend or retract a hydraulic cylinder which raises or lowers the distal end of the bridge.
An operator operates the height adjustment mechanism by a control in the cab which operates the motor in the mechanism. Some bridges have a motor control which incorporates a joy stick. The joy stick enables an operator to control the motor to raise or lower the cab by moving the joy stick forward or backward. Movement in one direction runs the motor in one direction and causes the height adjustment mechanism to elevate the bridge, and movement in the other direction reverses the motor and causes the mechanism to lower the bridge.
Before a cab engages an aircraft, the operator adjusts the height of the cab at the distal end of the bridge by moving the joy stick until the mechanism has properly aligned the cab with the aircraft door. With some systems, the operator must visually determine the proper position of the cab with respect to an aircraft door and move the joy stick until the mechanism has moved the cab to the proper position.
Some passenger loading bridges are equipped with controls which automatically cause the height adjustment mechanism to move the cab to a predetermined height. One type of automatic control for a vertical height adjustment mechanism includes an electric control which has a console equipped with a number of push button type switches, each of which is labelled with the name of a different type of aircraft. Actuating a switch causes the mechanism to move the bridge column to a preset location so that the cab is properly aligned with the the door of the type of aircraft named on the switch label. Each switch in the console is connected to a mechanically actuated switch located adjacent the bridge column. When a switch is actuated, the bridge is moved until a cam mounted on the bridge column trips the mechanical switch, which interrupts power to the motor. The cam is positioned to trip the switch when the bridge reaches the preset position.
A problem with a control which incorporates a mechanically operated switch mounted on the bridge drive column is that it is difficult to adjust the cam which operates the switch. The cam is positioned on the bridge column which is beneath the bridge and is relatively inaccessible. Any adjustment must be done from underneath the bridge.
It is desirable to provide a control in which an operator can move the distal end of a passenger loading bridge to a preset position to accommodate a particular aircraft by actuating a switch.
It is also desirable to provide a control which enables the preset position to which the bridge is moved by the height adjustment mechanism when a switch is actuated to be easily changed by a mechanism accessible fron inside of the bridge.
It is further desirable to cause the height adjustment mechanism to move the bridge only if the operator continuously engages a switch in the control and to stop the bridge from moving if the operator releases the switch before the bridge is at the preset position. This is to prevent an operator from walking away from the control when the bridge is moving, since it is desirable to have the operator in a position to avert an accident in the event of a system malfunction whenever the bridge is moving.